Researchers believe that the rapid spread of the Delta variant Covid-19 could be due to a key amino-acid mutation within the SARS-CoV-2 spike proteins.
The SARS-CoV-2 Delta variant of SARS has quickly replaced the Alpha variant all over the globe. The Delta variant was first discovered in India in late 2020 and is believed to be at least 40% more transmissible than that found in the UK last year.
The mechanism driving this global replacement is not yet known.
The study is still being peer-reviewed, and will be posted on bioRxiv’s preprint server bioRxiv. It showed that the P681R mutation within the Delta spike plays an important role in the replacement Alpha-to-Delta variation.
Researchers from the University of Texas and others wrote the abstract: “Delta SARS–CoV-2 effectively outcompeted Alpha variant in human lung epithelial cell and primary human bloodway tissues.”
Nature reported that the P681R mutation is located in an area of spike protein known as the furin site.
A shorter string of amino acids, P681R, is linked to increased infectivity in viruses like influenza. It has never been detected in sarbecoviruses, the coronavirus family to which SARS-CoV-2 is a member.
Pei-Yong Shi, a virologist at Galveston’s University of Texas Medical Branch, stated that “The key characteristic of Delta is the fact that transmissibility seems like it is ramping up to the following notch.”
Shi said, “We thought that Alpha was quite bad. Very good at spreading.” Shi said that this one appears to be even worse.”
In cultured human-airway epithelial cells, which were infected with the same number of Alpha and Delta viral particles, the Delta variant was able to quickly outcompete the Alpha variant. The advantage Delta enjoyed was diminished when the team removed the P681R mutant.
Nature reported that the study suggested that mutations can also speed up the spread SARS-CoV-2 cell to cell.
Researchers from the University of Tokyo discovered that spike proteins containing the P681R mutation fuse with plasma membranes of infected cells almost three times faster that spike proteins without the mutation. This is a crucial step in infection.
The team believes that the P681R mutation is not the only one. Further research is needed to study other mutations in Delta’s spike protein to better understand how it transmits.